X Factor bosses are investigating problems with its voting app after viewers accused the ITV show of a "fix" when they were unable to use it during Sunday night's show.

Viewers struggled to use the app as they attempted to register their lifeline vote to save either Sam Lavery, Four Of Diamonds or Saara Aalto.

Four Of Diamonds eventually became the latest act to be eliminated, after going up against Aalto in a tense sing-off.

Viewer were angry that the app crashed at a crucial moment (Image: ITV)

Susan Perry wrote on Twitter: "X Factor app not logging in for me or any of my friends - fix!!!"

Laura Colley wrote: "X factor is such a fix! The app has crashed and won't let anyone vote."

Amy Ryans wrote: "When the X factor app won't let you log in to vote because it knows you're not going to vote for Sam £liberty £fix"

-paigegrant wrote: "X factor app not working absolute fix."

An X Factor spokesman said: "We are aware there were some problems reported during the lifeline vote and we are looking into it."

Four Of Diamonds - who only got together a week before they auditioned for the judges - admitted they were a bit "lost for words" after getting their marching orders but said it had been a wonderful experience.

Ryan Lawrie went straight through this week having been in the bottom three for three weeks in a row (Image: Syco/Thames/Dymond)

They added: "It is a huge platform for us to get out into the industry. We are so grateful for the opportunity."

Viewers also accused contestant Ryan Lawrie of miming his vocals, after seeing him singing with the microphone held away from his mouth.

But an X Factor spokesman said: "All contestants sing live and no-one mines. Ryan's mic was live throughout his performance."